Milo g



(No Model.)

' M. G. KELLOGG.

MULTIPLE SWITGHBOARD.

No. 592,323. Patented Qllet. 26,1897.

Ens co; Immo-mko l ZJ UNTTED STATES PATENT OFFICE.

MILO G. KELLOGG, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE KELLOGG SWITCI-IBOZARD AND SUPPLY COMPANY, OF SAME PLACE.

MULTIPLE SWITCHBOARD.

SPECIFICATION'forming part of Letters Patent No. 592,323, dated October 26, 1897. Application filed November 29, 1889. Serial No. 332,026. (No model.)

To @ZZ whom t may concern:

Be it known that I, MILO G. KELLOGG, of Chicago,Illinois,temporarilyresiding atStuttgart, in the Empire of Germany, have invented certain new and useful Improvements in Multiple Switchboards for Telephone-Exchan ges, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

My invention relates to single-circuit telephone -linesg and it consists in a system ot' testing such lines to determine whether they are in use.

In the accompanying drawings, illustrating my invention, Figures la and lb are front views of sections of two multiple switchboards to which the same lines are connected. Fig. 2 is a diagram illustrating the main-line switchboards, apparatus, and connections necessary to illustrate my invention. Fig. 3 is a diagram of an operators cord system to be used in connection with the boards. Fig. l is a diagram of a subscribers-station apparatus. Fig. 5 shows an operators test system.

In the gures like parts and apparatus are designated by the same letters and numerals of reference.

G represents the ground connection.

In Fig. 2, A is a sectional view of the switchboard shown in Fig. l, and A is a sectional view of the board shown in Fig. 1b, each as indicated by the line d e.

There are as many boards in the exchange as are necessary for the number of lines. On each board is a spring-jack or similar switch for each line. Each switch hasacontact-spring which normally bears on an insulated contact-point and has a contact-piece insulated from the rest (except by the circuit connections) and is adapted to receive a switch-plug and, when a plug is inserted, to disconnect the spring from the contact-point and form connection between the spring and the contact-piece of the plug.

In Fig. 2, g g represent the springs of the different switches, h h the contact points, and jj the contact-pieces. Z Zare the switchholes. a b are the rubber pieces on which the metal parts are mounted and through the fronts of which are the holes Z Z. These holes are adapted to receive the switch plugs, (shown in Fig. 3,) and when a plug is inserted to operate the switch, as above described.

The contact-piecesjj should be so placed that a test-plug may be readily applied to them. Their function is to form test-pieces for their lines on the different boards, and they may be placed as shown, or in other convenient positions on the boards.

The subscribers-line connections are shown in Fig. 2, each line passing through test-contactsj, thence through the pairs of contacts g Z1. in the order named, thence through a resistance and annunciator w to ground at G. The order of the resistance and annunciator is immaterial. The resistance may be in the annunciator or the annunciator may be omitted and some other equivalent method of calling be used. The resistance may be a coil or any substantial equivalent. Under these conditions a plug D may be inserted either way into a jack and make connection with either test-contact j or springcontact g. The order of the contacts gh may be reversed and the plug so inserted into the jack that its contact n makes connection with the test-contactj, thus establishing a connection with the line conductor.

Fig. 3 shows an operators cord system. Two plugs D, composed of insulating material m, have contacts n so mounted as to make connection with a test-contactj or springcontact g whenv inserted in a jack and to make connection with a base-plate o, grounded at G when resting in their normal position. The contacts of the two plugs are connected together by a flexible cord conductor CZ, in the circuit of which is a looping-in switch Y, adapted to be placed upon either of the pairs of contacts q q r 1' s s, and thereby loop in a clearing-out annunciator fo, a call-generator B, or an operators telephone set t. When in use, the circuit of the looping-in switch Y is completed over two connected line-circuits or over one connected line-circuit and ground G through the base-plate o. The switch Y normally rests upon the contacts q q, looping in the clearing-out annunciator fu, there being a separate annunciator individual to each IOO generator'may be common to all or only some of the pairs of plugs of the exchange, the connections being apparent to Those skilled in eral thousand ohms, and the resistance in the the art.

Fig. 4 shows one of the many possible arrangements ofthe subscribers outfit that may be used in my invention. normally runs through the bells 2, the short The line conductor r' circuit 15, and contacts p q, around the generator 1, thence lby conductor 14 to -the switchlever 4, contact 9, short circuit 13, around the i receiver set to ground at G. The resistance the telephone is o' the switch and is thus switchedfor use, the circuit of the line convof. the circuit being mostly in the bells 2 is l ordinarily about yone hundred ohms. When hundred ohms. many ohms to this circuit as des'ired.

The resistance 9 may add as i It may be a 'coil `or any'other substantial equivalent. While the Vtelephone is switched for use, the l circuit vof the transmitter 5 and battery 8 is .l closed through the primary coil 6, contact 10, i lever 4, 'and conductor 14. This lever 4 is preferably, though not necessarily, the usual automatic switch. When the telephone is on its switch and the generator is operated, it cuts itself into4 line-circuit by opening thei pair of contacts p q automatically in the usual It will be noticed that normally, vor when the telephone is not switched for use, the subv comprising 'a test-plug T, a test receiving instrument S, and a test-battery B', all grounded at G. The order of the test receiving instrument and battery is immaterial unless one battery is used for two or more test receiving instruments and plugs, in which case they should be'connected in the lorder named.

' The instrument and battery are adjusted to each other and the other parts as follows: They are of such strength that when closed to the circuit ofa line through a test-piece j and the line is not switched atiany board and the subscribers telephone is on its switch enough current will pass through the instrument and to ground through the office ground and the station groundof the line to operate the instrument; but when the line is switched for use at any board and the circuit to the oftice ground is open or when the additional resistance is placedin the-line-circuit by the subscribers telephone being taken from its switch enough current will not 'pass through the vinstrument to operate it. The resistance in the ground-circuit of aline may without inconvenience be made several hundred ohms, as the generators are commonly made to operate the annunciators over resistances of sevmay be made, as required or convenient, to

.produce the test operations on the test receiv ing instrument, as above indicated.

The necessary resistance required to bel placed in theI ground-circuit of each line at the central office might be included in the line annunciator-coil.

The test depends on the lfact that an electromagnet with an armature and a suitable retractile springV may be made to operate -or move the armature when closed in circuit with a battery of given strength through a comparatively small resistance and not to move 'the armature when the resistance is lconsiderably increased. This adjustment and operation would be determined by and depend on the style of the electromagnet, the strength of the retractile spring, the size of the battery, and the resistances of the circuits. The adjustments to obtainl the required test operations are easy to obtain. For instance, the resistance in the line-circuits in exchanges of ordinary character may be made about live hundred ,ohms for each line when the subscribers telephone is not switchedfor use and, say, one thousand ohms when the telephone is switched for use, and the resistance in the circuit of each line between its test contact-pieces and the normal j ground connection may be,'say, three hundred ohms. The test-bell may have, say, one hundred ohms resistance and a suitable adjustable retractile spring. Ten or twelve cells of test-battery might be used. When the operator makes the test of a line by applying the test-plug to the contact-piece j oi the line and the line is not switched with another line at the central office and its subscr'ibers telephone is not switched for use, the resistance of the test-circuit (exclusive of the operators test system) Vwould be about one hundred and eighty-seven ohms and the test receiving instrument would sound. Should, however, the subscribcrs telephone be switched for use, (the line not yet being switched,) s uch resistance of the test-circuit would be increased to about two hundred and thirty ohms and the instrument would not sound. Should the twolines be connected together and their telephones be switched for use, the resist-ance of the test-circuit (exclu- IOOv IIO

sive of the operators test system) would be about live hundred ohms. Should the lines be connected together and only one of the 'telephones be switched for use, the resistance Wouldbe about three hundred and thirtythree ohms, and should neither telephone be switched for use the resistance would be about two hundred and fifty ohms. In any of these cases the resistance is so much greater than that when neither the line nor the telephone is switched for use that the required test operations and adjustment would be easy to obtain.

The operators telephone set is so constructed as to have a high resista-nce, so that when connected on one side of the line-circuit being tested and on the other to groundA through a plug D, resting on abase-plate o, the test receiving instrument of the testing operator will not respond and will thus indicate that the line is free. W'hen an operator, therefore, makes a test of a line by placing the test-plug on the line test-piece and the line is not switched for use and the telephone is on its switch, the test receiving instrument will respond, indicating that the line is free If, however, either the line is switched for use, or the subscribers telephone is off from its switch for use, the instrument will not respond, indicating that the line is not free.

In multiple-switchboard systems an operator to whom certain lines are assigned to answer frequently receives several calls at practically the same moment, and it may require some time before she can switch to a certain line and answer its call. In systems in which the test depends only on the line being switched at some board another operator may, in the meantime, test the line, and nding it to test free may switch it with another line and cause annoyance and confusion to the subscriber. This cannot occur in this system of testing, because as soon as the subscriber takes his telephone from its switch the line will test busy whether or not it is switched at the central oflice. Again, in systems of testing which depend only on the subscribers telephone being on or oft its switch confusion frequently arises from the fact that a subscriber places his telephone on its switch when he is through conversation without sending in a clearing-out signal, and his line tests free and is connected to when it is already switched with another line. Lines in this condition are technically called tied up. Lilies4 cannot become tied up in this system, because the line will test busy until it is disconnected at the central oiiice, whether or not the subscribers telephone is on its switch. The system therefore combines the advantages and obviates the disadvantages of the two general systems of testing outlined above.

It is obvious that instead of a ground connection any other common conductor may be substituted. There may be a common wire connected to all the wires shown as grounded, or each circuit may have a return metallic conductor, all said conductors being joined together at central and connected to the lwires shown as grounded.

I claim as my invention and desire to secure by Letters Patent- 1. A test-circuit for a subscribers line, from the office ground through a test receiving inmally in contact but separated while the line is switched at their board and through a resistance and in the other direction to the subscribers ground through his station apparatus and a switch having contacts and connections at the subscribers station to switch a comparatively high resistance into the circuit of the line while the telephone is switched for use and a comparatively low resistance while the telephone is not thus switched, said test receiving instrument being so adjusted to the battery and the circuit that it will sound when on a test being made neither said telephone nor the line is switched for use, substantially as set forth.

2. A test-circuit fora subscribers line, from the oflice ground through a test receiving instrument and battery to a test-plug, thence to a line-contact when the test is applied, thence in one direction to the ofiice ground through a series of pairs of contact-points, one pair on each of several boards', each pair normally in contact but open while the line is switched at their board and through a resistance and in the other direction to the subscribers ground through his station apparatus, and a switch having contacts and connections at the subscribers station to switch a comparatively high resistance into the circuit of the line while the telephone is switched for use and a comparatively low resistance while the telephone is not thus switched, said .test receiving instrument being so adjusted to the battery and the circuit that it will sound when on a test being made neither said telephone nor the line is switched for use but not otherwise, substantially as set forth.

3. A test-circuit for a subscribers line, from the office ground, through a test receiving instrument and battery to a test-plug, thence to -a line-contact when the test is applied, thence, in one direction, to the office ground through a pair of switch contact-points normally in contact but separated while the line is switched at their board, and through a resistance and, in the other direction, to the subscribers ground through his station apparatus, and a switch at the subscribers station with contact-points which switch his telephone, 'secondary of induction-coil and a resistance into the circuit of the line while his telephone is switched for use and a signalbell into the circuit while the telephone is not thus switched, said test receiving instrument being so adjusted to the battery and the circuit that it will sound when on the test being made neither said telephone Anor the line is switched for use but not otherwise, substantially as set forth.

4L. In a telephone-exchange system, a subscribers line normally grounded through a pair of switch-contacts and a resistance at the central office, a test-piece for the line con- IOO IIO

nected to the line between the subscribers station and the pair of switch-contacts, a callbell normally in the normal ground connection of the line-circuit at the subscribers station the subscribers telephone and switch, and contacts and connections whereby an increased resistance is included in the line-cir'- cuit when said telephone is removed from the switch, in combination with a test instrument and battery at the central office grounded on one side and connected on the other side with a test-plug adapted to be brought into connection with the test-piece of the line.

5. Atest-circuitforasubscribersline, from the office ground, through a test receiving instrument and battery to a test-plug, thence to a line-contact when the test is applied, thence, in one direction to the office ground through a series of pairs of contact-points, one pair on each of several boards, each pair normally closed but open while the line is switched at their board and a resistance, and, in the other direction, to the subscribers ground through his station apparatus, in combination with a switch at the subscribers station with contact-points which switch his telephone, secondary of induction-coil and a resistance into the circuit of the line While said telephone is switched for use and the signalbell into the circuit while the telephone is not thus switched, said test receiving instrument being so adjusted to the battery and the circuit that it will sound when on the test being made neither said telephone nor the line is switched for use but not otherwise, substantially as set forth.

6. In a telephone-exchange system, a subscribers line grounded at its outer end and having in its circuit at the subscribers station a comparatively high resistance While hisvtelephone is switched for use and a comparatively low resistance while the telephone is not thus switched, and at the central office a switch with a pair of contact-points normally in contact but open while the line is switched by it, a test contact-piece insulated from the rest (except by the circuit connections), and a resistance grounded on one side, said line passing through said pair of contact-points and thence to the other side of said resistance and said test oontactpiece being connected to the line before the line passes to said contact-points, in combination with a test wire or circuit, containing a test receiving instrument and battery, grounded at one end and connected at its other end to a test plug or device adapted to be brought tion a comparatively high resistance while the telephone is switched for use and a comparatively low resistance while the telephone is not thus switched, and at the central ofiice a series of switches, one switch on each of several boards, each switch having a pair of contact-points normally closed but open while the'line is switched at their board, a test contact-piece insulated from the rest (except by the circuit connections), and a resistance grounded on one side, said line passing, successively through said pairs of contact-points and thence connected to the other side of said resistance, and said contact-piece being connected to the line before the line passes to said pairs of contact-points, in combination with a test wire or circuit containing a test receiving instrument and battery, grounded on one side and connected on its other side to a test plug or device adapted to be brought for testing into connection with said test contactpiece, said instrument being so adjusted to the battery and circuits that it will sound when on the test being made neither said telephone nor the line is switched for use but not otherwise, substantially as set forth.

.8. In a telephone-exchange system, a subscribers line normally grounded at its outer end and at the subscribers station, a switch with contact-points to switch his telephone, secondary of induction-coil and a resistance into the circuit of the line while said telephone is switched for use and the signal-bell into the circuit While the telephone is not thus switched, and at the central ofiice a switch with a pair of contact-points normally in contact'but open while the line is switched by it, a test contact-piece insulated from the rest (except by the circuit connections) and a resistance grounded on one side, said line passing through said pair of contact-points and thence to the other side of said resistance and said contact-piece being connected to the line before the line passes to said contactpoints, in combination with a test Wire or circuit containing a test receiving instrument and battery, grounded on one side and connected on its other side to a test plug or device adapted to be brought on testing into connection with said test contact-piece, said instrument being so adjusted to the battery and circuits that it sounds when on a test being made neither said telephone nor the line is switched for use but not otherwise, substantially as set forth.

9. In a telephone-exchange system, a subscribers line grounded at its outer end and having in its circuit in the subscribers station, apparatus of comparatively high resistance while his telephone is switched for use and apparatus of comparatively low resistance while the telephone is not thus switched, in combination with a test contactpiece at the central ofce permanently connected to the line, a resistance normally connected on one side to the line and connected loo IIO

on the other side to the ground, switch contact-points which disconnect the line from said resistance while the line is switched for use,and a test wire or circuit containing a test receiving instrument and battery, grounded on one side and connected on its other side to a test plug or device adapted to be brought for testing into connection with said test contact-piece, said instrument being so adjusted to said battery and the circuits that it sounds when on the test being made neither said telephone nor the line is switched for use but not otherwise, substantially as set forth.

l0. In a telephone-exchange system, mul

tiple switchboards, a subscribers line grounded at its outer end and having in its circuit at the subscribers station, apparatus of comparatively high resistance while his telephone is switched for use and apparatus of comparatively low resistance while the telephone is not thus switched, and at the central office a series of test contact-points, one on each of the multiple boards and connected to the line, a resistance connected on one side to the ground and normally connected on its other side to the line, and switch contactpoints which disconnect the line from said resistance while the line is switched for use, in combination with a test wire or circuit at each board containing a test receiving instrument and battery, grounded at one end and connected at its other end to a test plug or device adapted to be brought for testing into connection with said test contact-piece, said instrument being so adjusted to the battery and circuits that it sounds when on a test being made neither said telephone nor the line is switched for use but not otherwise, substantially as set forth.

1l.. In a telephone-exchange system, multiple switchboards, a telephone-line grounded at its outer end and having at the subscribers station, apparatus of comparatively high resistance in its circuit while his telephone is switched for use and of comparatively low resistance while it is not thus switched, test contact-pieces, one on each board and each connected to the line permanently, switches for the line one on each board and each containing` a pair of contact -points normally closed but open while the line is switched at their board, and a resistance grounded on one side, said lino passing, successively, through said pairs of contact points and thence connected to the other side of said resistance, in combination with test receiving instruments, one at each board and grounded on one side and connected on its other side to a test plug or device adapted to be brought for testing into connection with the test contact-piece at its board, said instruments each having a battery in its testcircuits and being so adjusted to the battery and the circuits that it sounds when on a test of the line be.

ing madeneither the telephone nor the line is switched for use but not otherwise, substantially as set forth.

In witness whereof I hereunto subscribe my name this 18th day of October, 1889.

MILO G. KELLOGG.

lVitnesses:

FRANCES D. KELLoGG, MARGARETHA RIEHL. 

